Use a Satellite TV Dish as a WiFi AntennaRepurpose the Junky Old Dish
A satellite dish is a powerfull signal booster when used in combination with a WiFi biquad antenna. I see lots of satellite dishes laying in trash when driving. Grab one next time you see an old dish laying on the sidewalk.
I have tried using both smaller Dish Net dishes and larger 76cm (30 inch) dishes [Fig. 1]. They both work well. The larger dish will give you some extra gain but even the small one works really well. How far you can go with this booster? I have tested it up to 250m (820 feet) with Netgear router on the other end and it worked flawlessly. The router was using the stock antenna it came with.
Fig. 1 Large (76cm) dish with a biquad antenna
First disconnect the so called LNBF from the dish [Fig 2]. Then mount your biquad antenna in place of the LNBF. Ideally, it should be in the exact same position as this is the focal point of the parabolic dish.
Fig. 2 Dish 500 and LNBF
You can mount the "naked" biquad [Fig. 3] or place it in an enclosure first which will protect it from weather [Fig. 4].
Fig. 3 Unprotected biquad antenna will corrode outdoors
Fig. 4 This antenna was housed inside an enclosure and it did not corrode
The actual rigging method is something you'll have to decide based on the materials you have. I tried mounting the antenna directly to the arm of the dish [Fig. 3]. This method works well but all exposed copper pieces will oxidize quickly. In addition, an exposed antenna can be easily damaged should the dish lose footing.
A better way is to house the antenna in an enclosure and mount it using a support made of PVC electrical conduit pieces [Fig. 5]. This method was useful on a Dish Net parabolic dish to elevate the position of the antenna. Dish Net dishes have a chunky LNBF that sits up high so anything you can do to lift the position of your antenna and make it close to where LNBF sits will help.
Fig. 5 Mounting biquad antenna on Dish 500
Make a provision to rotate the antenna 90 degrees [Fig 6]. The ability to rotate 90 degrees will allow you to match the polarization of the distant antenna you're connecting to.
Fig. 6 Biquad antenna polarization
All satellite dishes are designed to point up to the sky. Even when the dish is seemingly 90 degrees to the ground it is still looking up. To properly aim the beam you will need to point the dish down [Fig. 7]. If you are on a hill you will need to point down even more.
Fig. 7 Dish 500 fitted with WiFi antenna looking down
Now it's only a matter of fine tunning the position of the dish. Using a free tool like Netstumbler is a good way to aim your dish properly. Once you lock the maximum signal tighten the screws on the dish and rotate the antenna 90 degrees. One of the two polarization positions will give you stronger reception.
[size=-1]Securing the dish with bricks like I'm doing in this picture is a very bad idea. Winds can easily knock the dish down or lift it off your roof. Use something heavy to hold the dish down while locating a good spot to place it. Once you find the spot mount the dish permanently with heavy screws.
[size=-1]Finally, there may be regulations determining maximum signal strength for 2.4GHz frequency in your country. In the United States FCC regulates such matters. You can find out official FCC information here. It is not likely that FCC would take any action unless they receive interference complaints from people or business in your signal path. Also, this setup is fairly limited and without powerfull amplification you will probably not bother anyone.
这个老外在另外一篇文章里描述了双菱馈源的做法，也是鸟文，一并发出供大家参考
Housing for WiFi Biquad AntennasProtect Your Outdoors Antenna
[size=-1]Two types of damage can affect a working antenna.
[size=-1]It can sustain physical impact and the copper wire may bend and break the soldiered point.
[size=-1]If exposed to rain the copper will oxidize which may eventually lead to decreased performance. The antenna pictured in Fig. 1 was used outdoors for a month in almost no rain. The antenna on the right was used for the same amount of time in the same location but was enclosed. The difference is striking [Fig 2].
Fig. 1 Oxidation after a month of use
Fig. 2 This biquad was housed
[size=-1]Both of these types of damage can be easily mitigated with proper antenna housing. You can use ready made electronics enclosures or even low end solutions like Tupperware containers. If you use Tupperware consider sealing it with silicon to prevent rain from getting in.
[size=-1]The enclosure can not be made of metal nor can have any metal foil decals on it. You must use a material that does not reflect microwaves.
[size=-1]Some materials may cause the signal strength to drop. You can conduct a simple test of microwave attenuation of your desired enclosure. Lock the antenna into a vise grip or a camera tripod and point it towards a distant access point. Connect the antenna to the computer and start Netstumbler. Run Netstumbler for several minutes. Then place the antenna housing in front of the biquad and observe the signal change in Netstumbler. If there is no change or change is rather small your box is acceptable as an antenna enclosure.
[size=-1]
[size=-1][size=-1]You can find equipment enclosures at electronics stores or mail order them. Polycase has a great selection of various enclosures and I used their products for other projects. The actual enclosure I used here is CM5-125 from Pactec. It's a little tight for Martin's biquad so I ended up belt sanding the edges of the PCB to make it fit in the box. The change of size does not seem to affect the antenna performance.
[size=-1]Drill small holes in the biquad PCB to match the hole configuration in the enclosure [Fig. 3]. Place the antenna face down into the enclosure [Fig 5]. Drill a center hole into the back of the enclosure so you can run the cable through it. I used a foamy ring from a 50 CD-R spindle as a gasket between the back of the antenna and the back of the enclosure [Fig. 6].
[size=-1]You will notice that the construction of the biquad pictured here differs slightly from Martin's design but the same steps are valid for an antenna built exactly to his specifications.
Fig. 3 Drill holes to match the housing mount
Fig. 4 enclosure
Fig. 5 Place the antenna in the enclosure
Fig. 6 CD spindle foam ring
Fig. 7 Job done
Fig. 7 Professionaly looking antenna
[size=-1][size=-1]I strongly recommend using heat shrink tubing to protect the antenna's soldiered connections from being ripped apart. The LMR 400 cable is very rigid. Since it can not flex much it can not absorb physical abuse and your point of soldier may fail. Shrink tubing is a special type of material (you can find it at Radio Shack) which will shrink when exposed to heat generated by a heat gun or a gas torch.
[size=-1]Prior to soldiering your "N" connector, dress the cable and the copper pipe with heat shrink tubing. Mount and soldier the connector and then shrink the tubing so it wraps tightly over the pipe and the cable. The other piece should cover the connector and the cable right next to it.
[size=-1]If you don't have a heat gun you can use the propane torch but have to be carefull not to burn the cable and the shrink wrap. Test it on a small area first.
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发表于 2009-10-31 12:47
期待论坛高人出手翻译，好资料不敢独享，放出供各位一起学习，资料来之不易，收点手续费应该不过分吧，呵呵
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千斤顶
显身卡
发表于 2009-10-31 13:23
